1. Field of the Invention
The present invention relates to a laser oscillation method and a laser device, and more particularly to a laser oscillation method and a laser device suitable for using in fabricating a laser medium that is pumped by pumping light to perform laser oscillation.
2. Description of the Related Art
Conventionally, usefulness of a neodymium doped gadolinium-vanadate (hereinafter, referred to as ‘Nd:GdVO4’ accordingly) crystal, which is a gadolinium-vanadate (GdVO4) crystal to which neodymium (Nd) as laser active ion has been added (hereinafter, referred to as ‘doped’ accordingly), as a laser medium has been expected.
However, fabrication of the Nd:GdVO4 crystal is difficult, crystal growth of the Nd:GdVO4 crystal is currently performed only on a research level, and it has rarely been commercially produced.
On the other hand, it has been pointed out that the Nd:GdVO4 crystal that is on production and sold has doping concentration of neodymium at 1% or less in the atomicity ratio, that is, low doping concentration of neodymium. Further, it has not guaranteed sufficient optical characteristics.
For this reason, when it is compared with a neodymium doped yttrium-aluminum-garnet (hereinafter, referred to as ‘Nd:YAG’ accordingly) crystal and a neodymium doped yttrium-vanadate (hereinafter, referred to as ‘Nd:YVO4’ accordingly), which have the same laser oscillation wavelength region as that of the Nd:GdVO4 crystal and currently hold a dominant share of the market as a solid state laser medium, the Nd:GdVO4 crystal has not completely made full use of its advantage nor has it been dominant in the market yet.
Furthermore, since it has conventionally been difficult to dope neodymium as laser active ion in high concentration exceeding 1% in atomicity ratio when fabricating the Nd:GdVO4 crystal, laser oscillation pumped by pumping light in a wavelength band other than the wavelength of 808 nm, which is the main absorption band of the Nd:GdVO4 crystal, has not been put into practical use until now.
In other words, since the Nd:GdVO4 crystal currently sold in the market, whose doping concentration of neodymium is low, has low absorption level of pumping light totally, it is difficult to be pumped in a wavelength band other than the main absorption band that is the wavelength of 808 nm. Therefore, even if it is pumped to perform laser oscillation, efficiency is poor due to small absorbable energy and thus output has not been effectively obtained.
For this reason, proposal of the followings has been strongly desired: a fabrication method of the Nd:GdVO4 crystal as a laser medium to which neodymium is doped in high concentration exceeding 1% in atomicity ratio; a laser oscillation method that uses the Nd:GdVO4 crystal, to which neodymium is doped in high concentration exceeding 1% in atomicity ratio, as the laser medium; and a laser device that uses that uses the Nd:GdVO4 crystal, to which neodymium is doped in high concentration exceeding 1% in atomicity ratio, as the laser medium.
It is to be noted that, in this specification, the Nd:GdVO4 crystal to which neodymium as laser active ion is doped in high concentration exceeding 1% in atomicity ratio is simply referred to as a ‘highly concentrated Nd doped GdVO4 crystal’ or a ‘highly concentrated Nd:GdVO4 crystal’, accordingly.
Further, due to the same background as the foregoing, proposal of the followings has also been strongly desired: a fabrication method of single crystal as the laser medium to which Tm, Ho, Er or Cr ion as laser active ion is doped in high concentration, such as Tm:YVO4 and TM:GdVO4, for example; a laser oscillation method using the single crystal as the laser medium; and a laser device using the single crystal as the laser medium.